The cleaning of structures having metallic surfaces can often pose various challenges. This is especially the case after fabrication, when complex residues may be found on the surfaces of the structure. Such residues may contain, for example, macroscopic and microscopic metallic particles produced by cutting and smoothing processes during fabrication; organic oils, greases and other lubricants used during fabrication; various fibers from fabrics used in initial cleaning and handling of the structure; and microscopic particles and fibers from the environment. These residues are often a combination of materials. Particulate residues embedded in heavy organic greases usually cannot be removed by washing with water because water will not dissolve or displace the grease. Some solvents that dissolve or displace the residues are generally either too expensive to apply on a large scale or they are a threat to the environment, such as ozone depleting chemicals.
Further, the cleaning of the interior wall surfaces of large container structures can be challenging, especially when it is necessary to precision-clean such surfaces, i.e. to remove not only macroscopic quantities of metal particles, hydrocarbons, and other residues, but also microscopic quantities of such residues. This is the case with the booster tanks of space launch vehicle booster propellant tanks. The inner wall surfaces of such tanks may not to be smooth surfaces. Instead, in some instances, the inner wall surfaces of launch vehicle propellant tanks are complex, having a multiplicity of ridges and test components that extend radially inwardly away from the walls into the internal containment area of the tank, and that may abut or intersect to form corners. Particles and organic residues remaining after the launch vehicle propellant tank fabrication process may adhere to and become lodged against these ridges and components and the corners formed by them, making cleaning difficult. The inner wall surfaces of launch vehicle propellant tanks having an isogrid structure are especially prone to this problem. Such tanks may be fabricated from aluminum panels. Achieving an isogrid structure (e.g., for lightweight and structural strength considerations) on the inner wall surfaces of the panels may involve a process of "hogging out" large quantities of aluminum, leaving numerous large and small aluminum particles on the panels. In addition, the process of hogging out the panels may employ various organic lubricating oils and greases, such that residues of these materials are also left on the inner wall surfaces of the panels making up the launch vehicle propellant tank. Wiping the inner wall surfaces with solvent dampened fabrics removes a significant quantity of these residues. Yet, such physical methods of cleaning are generally not sufficient to precision-clean the surfaces to be substantially free of macroscopic and microscopic residues and are not practical to clean large structures like launch vehicle tanks. In addition, the common practice of physically wiping the inner wall surfaces of launch vehicle propellant tanks may leave behind fibers from the fabric cloth or pad used to wipe the panels. The presence of even small quantities of such residues can cause a fire hazard when the launch vehicle propellant tanks are filled with liquid oxygen. Also, such residues can cause degradation in the performance of the propellants so affecting the efficiency of the launch vehicle's rocket engine.